A plane bound for San Francisco from Heathrow was delayed for hours after a mouse was found inside the aircraft.

Passengers aboard British Airways BA285 were already waiting for takeoff on Monday when the crew announced that the flight had to be grounded.

“A rather unusual occurrence has occurred,” an announcement was heard.

Travellers who were on the flight took to social media to report the incident,.

"Just had my flight to SFO cancelled because of a mouse on board the plane. Could it not get a visa," tweeted Mark Watt, one of the passengers. 

"About to fly to SF. There is a mouse on the plane. We all must get off,” posted  @midlandsound.

Contacted by Gulf News, British Airways confirmed the incident and apologised for the delay, but not without making a pun out of what just occurred.

“With service and prices this good, we know almost everyone wants to fly with us to San Francisco…but on this occasion there was one very small customer who we had to send back to the gate.”

“Everyone holding their own passport is now on their way to California, and we are sorry for the delay.”

The flight was able to depart about four hours later.